Paper-machine felt



United States Patent 0 3,224,923 PAPER-MACHINE FELT Thomas Hindle,Thornlea Beardwood Brow, and Edward Race, Langdale, Meins Road, both ofBlackburn, England No Drawing. Filed Aug. 8, 1960, Ser. No. 47,956Claims priority, application Great Britain, Aug. 13, 1959,

27,662/59 4 Claims. (Cl. 16164) This invention pertains to woven textilefabrics, in particular to fabrics useful as a paper-machine felt such asis employed in the manufacture of pulp, paper, board, asbestos-cementsheets, pipes and similar or related products. The material, inaccordance with the present invention, may be woven flat and then madeinto an endless band such as a paper-machine felt by joining the ends ofa pre determined length of the woven fabric, or it may be initiallywoven as an endless band in accordance with well known weavingprocesses.

According to customary, prior practice, these felts were manufacturedentirely from wool yarns, or, particularly in the case of the felts usedin the production of asbestos-cement products, from a combination ofwool and cotton. With the advent of nylon, polyester and similarsynthetic fibres, it was found that by manufacturing the felt from yarnscomposed of blends of wool fibres and synthetic fibres, theabrasion-resistance of the felts was greatly improved and the feltsexhibited a longer service life.

Whenever a paper-machine felt is composed entirely of wool or of amixture of wool and synthetic fibres, milling or fulling is an essentialoperation in the manufacture of the felt. Thereby, the weave structureof the felt, which otherwise would mark the paper, is masked at thesurface by the matted or felted wool fibres and yet its permeability towater remains of a high order.

Until recently, it was thought essential that the proportion ofsynthetic fibres incorporated in the felt must be less than that whichwould prevent appreciable milling or fulling of the felt. However, ithas been discovered recently that if such a felt, made wholly orpredominantly of synthetic fibres, has one or both of its surfacesraised, as by napping or gigging, and the raised fabric is subjected toa process of needling, the resultant fabric simulates closely enough amilled felt made wholly or predominantly of wool to be used as apaper-machine felt. The operation of needling is effected in any knownmanner, as by passing the woven fabric through a machine wherein thesurface of the fabric is frequently pierced by barbed needles, theresult being to force the nap fibres consituting the raised surface intothe body of the fabric.

Unfortunately, in many instances, prolonged needling is requiredeffectively to entangle the raised fiibres into the woven body of thefabric. Two major defects are liable to arise as a result of theprolonged needling operation. Firstly, serious reduction in the Waterpermeability of the felt is possible, and it is not unusual for thewater permeability of the felt after extensive needling to be onlyone-half of its initial value. This reduction in permeability has anadverse effect on the rate of drainage of water from the paper sheetthrough the felt when the latter is in operation on the paper-machine.Secondly, the process of prolonged needling the raised, woven fabricbreaks many of the fibres both of the raised surface and of the yarns inthe body of the felt. This weakens the fabric and makes it moresusceptible to degradation by mechanical abrasion.

The expression, endless woven fabric, as used herein, is intended toinclude not only fabric which is woven endless, initially Qthe weft inthe loom becoming the warp in the finished fabric), but also a length offabric, woven fiat, whose ends have been joined, and wherein the warpsand wefts of the fabric are the loom warps and wefts. In thisspecification by the term warp is, therefore, meant those yarns arrangedin the longitudinal direction of the endless finished product(regardless of how pro duced), such as a papermarkers dryer felt and bythe term weft is meant those yarns arranged in a direction which istransverse of the length of the finished product. The synthetic contentof the yarns may be in the form of a plurality of continuous filaments,or staple fibres thereof, and general references to synthetic fibres orfibres when they occur herein and in the claims hereof are inteded toinclude, within their scope, both forms.

Broadly stated, the object of the present invention is to simulate in apredominantly synthetic felt, the effect obtained when wool is felted.In the latter case, adjacent fibres become entangled one with another,and not only do fibres within the same yarn become entangled, but thesurface fibres of one yarn become entangled with the surface fibres ofadjacent yarns running parallel and with the surface fibres of yarnscrossing one another. Thus, in wool felting, adjacent fibres becomeattached to one another, and yarns are likewise attached to each otherat their crossing points. In accordance with the present invention,synthetic fibres which contact at crossing points are joined together byintegral bonds of the material of which they are composed.

One object of the present invention is to provide an adequatelywater-pervious woven fabric, for use as a papermachine felt, which iswholly or predominantly of synthetic fibre and which has not beensubjected to a needling or equivalent operation. A further object is toprovide a woven textile fabric sufficiently pervious to the passage ofwater and sufficiently flexible to function satisfactorily as apaper-machine felt and which consists, at least predominantly, ofsynthetic fibres and wherein, Whereever constituent synthetic fibres, incrossing, touch one another, they are integrally joined together attheir mutual points of contact. Claims to a method of producing a fabricof the type herein claimed are made in applicants copending applicationSerial No. 289,381, filed June 20, 1963.

Briefly stated the invention provides a novel woven fabric, adequatelywater-pervious and sufficiently flexible for use as a paper-machine feltand which is predominantly of synthetic fibrous material and having atleast one outer surface acceptably smooth for such use and whereinadjacent, crossing synthetic fibres are integrally bonded together attheir mutual points of contact. The fabric may be produced byinterweaving warps and wefts, predominantly of synthetic fibrousmaterial to form a woven structure acceptable for use as a paper-machinefelt, and thereafter subjecting the fabric to the action of a reagentwhich causes some, at least, of the constituent synthetic fibres tocoalesce where one fibre contacts another in crossing, whereby saidcontacting fibres are integrally and permanently bonded together. Morespecifically, the preferred reagent is an aqueous solution of aninorganic salt which, in concentrated form, is effective to gelsynthetic fibres employed.

In the case of fabrics made wholly or predominantly of nylon and/ oracrylic fibres, such as Orlon (a registered trademark, the property ofE. I. lu Pont de Nemours & Co.) or Courtelle (a regisered trademark, theproperty of Courtaulds Ltd), (both being acrylic fibres such as thosemade of polyacrylonitrile and copolymers thereof) suitable salts arecalcium and lithium bromides and calcium and magnesium thiocyanates. Inthe case of fabrics made wholly or predominantly of polyester fibres,such as Terylene (a registered trademark, the property of ImperialChemical Industries Ltd.) or Dacron (a registered trademark, theproperty of E. I. du Pont de Nemours & Co.), or containing a materialproportion of such fibres in addition to acrylic and/ or polyamidefibres, suitable salts are calcium and magnesium thiocyanates.

In accordance with a preferred procedure in the manufacture of thefabric herein claimed, there is first provided a woven fabric of astructure acceptable for use as a base fabric of a papermakers felt andconsisting, at least in major proportion, of synthetic fibre;impregnating the fabric with an aqueous solution of inorganic salt, saidsolution in response to natural forces tending to accumulatepredominantly at points where fibres contact in crossing one another,the solution being too weak, when first applied, effectively to act uponthe synthetic material but being such that it can be so concentrated insitu and without determent to the fabric that it will act upon some atleast of the synthetic fibres to gel them; progressively concentratingthe salt solution thereby intensifying the tendency of the solution tomigrate toward and accumulate at the points at which fibres cross andcontact one another until eventually the salt reacts with the fibres atsaid crossing points causing them to gel and coalesce and ultimately toform permanent bonds predominantly at the crossing points rather thanover the entire area of the fabric whereby the felt retainssubstantially the same degree of permeability to water as when woven,then washing the fabric to remove the salt, and drying the fabric sothat the completed fabric is devoid of any substance other than that ofthe yarns from which it was woven. Thereafter, the inorganic salt iswashed out ofthe fabric with water.

Since, according to the herein described method, the application of heatand pressure is not essential for bonding the fibres together, theconstituent yarns of the woven fabric are of substantially the samedegree of roundness as when the fabric was woven and the intersticesbetween the yarns are not reduced in area, as would result from theflattening of the yarns by the application of heat and pressure.

If a woven fabric for use as a paper-machine felt is composed of amixture of two synthetic fibrous materials,

then a salt capable of swelling and dissolving or gelatinising thesurface of both fibres is employed. For

example, if the fabric is composed of nylon and Terylene,

then calcium or magnesium thiocyanate is employed as the reactant.

The concentration of inorganic salt in the impregnating liquor can be aslow as 0.5% by weight, although for good fibre-to-fibre bonding, it ispreferred that a 2% to 5% solution is used, and the solution can, infact, have a concentration of inorganic reactant as high as by weight.

One example of the processing according to the invention is as follows:

An endless woven fabric of a structure suitable for use :as apaper-machine felt has warp and weft yarns spun from crimped nylonstaple fibres. The fabric is treated at ambient temperature for minutesin a 5% by weight solution of lithium bromide, 4 gallons of solutionbeing 'used for every 10 lb. of synthetic fiibre. The impregnated fabricis hydro-extracted and then dried on a felt-stretching machine, at leastone cylinder of which is heated. As

"the water evaporates from the felt, thus concentrating Furthermore, thefabric need not necessarily be woven wholly from spun synthetic yarnsand, as has been pointed out hereinbefore, the general references tosynthetic fibres and fibres herein and in the claims, are not intendedto be limited to the fibres of such yarns. For example, the warp yarnsmay be spun from crimped synthetic fibres, or from straight syntheticstaple fibres, or may be continuous filament synthetic yarns, orcontinuous filament bulked synthetic yarns of the non-stretch type, suchas Taslan-textured yarns, or yarns composed of a core of continuousfilament synthetic yarns around which is wrapped a finer Taslan-texturedyarn. (Taslan is a trademark registered by E. I. du Pont de Nemours &Co.). The weft yarns are preferably spun from synthetic staple fibres,but these staple fibres may be the commercially-produced crimpedsynthetic fibres, or they may be prepared by cutting into staple fibrelengths those commercially-produced continuous filament yarns which areknown as bulked yarns and stretch yarns and bulked and stretch yarns.

In accordance with the present invention, many of the synthetic fibresare integrally joined by bonds which occur predominantly at points atwhich fibres contact where they cross one another. It should beremembered that it is extremely rare to find two fibres in a spun yarnwhich make a line contact of appreciable length, although they mayrepeatedly cross each other. Since the migration of the liquid towardfibre-crossing points is at the expense of liquid which coats fibres atother places, the probability of forming bonds between fibres which aregenerally parallel, although closely adjacent, is very much reduced, sothat the present process does not result in stiffening or reducing thenormal flexibility of the felt to a degree such as to impair its utilityfor the intended purpose and does not substantially decrease the initialpermeability of the original woven fabric.

Moreover, the present fibre bonding process can be applied withadvantage to the wholly or predominantly synthetic paper-machine felts,described in our copending United States application Serial No. 47,955,filed August 9, 1960, now US. Patent No. 3,063,127, in which the weftyarns are spun from blends which contain shrinkable With felts for useon certain types of paper-machines it is preferred to raise, as .bynapping, one or both surfaces of the woven fabric before impregnationwith the reactant solution. In other instances, it is preferred first tobond the fibres by impregnation, evaporation of the entrained water andrewashing and thereafter to raise one or both surfaces. In this lattercase, although the operation of raising breaks some of the bonds on thesurface fibres, these fibres are still bonded below the raised surface,and the fibres of the yarns unaffected by raising are, of course, stillbonded to one another.

In either case, the nap fibres collectively mask the weave pattern andprovide a smooth surface.

I claim:

1. A papermakers felt consisting of material wherein uncoated warp andweft yarns are so intercalated as to provide a water-absorbent structureacceptable to constitute the base fabric of a conventional 'papermakersfelt, and wherein the Warp and weft yarns are of substantially the samedegree of roundness, in transverse section, as when freshly woven, thewarp and weft yarns being in major proportions, at least, of syntheticfibres; the felt possessing desirable characteristics of a conventionalwool felt including tensile strength, flexibility and permeability towater but possessing greater abrasive resistance and having a longerservice life than an all-wool felt, one face, at least, of the feltcomprising nap fibres which mask the weave pattern and collectivelyprovide a smooth surface of the kind desirable in paper making, the feltbing substantially devoid of any substance other than that comprised inthe original warp and Weft yarns, as woven, and being furthercharacterized in that, predominantly at points at which constituentfibres cross and contact one another, they are so coalesced from a gelstate as to form permanent bonds thereby connecting the yarns of whichthe united fibres are constituent elements whereby, although thematerial retains substantially the same degree of flexibility andpermeability which is possessed when first woven, it is comparable to afulled wool felt as respects the permanent union of constituent fibres.

2. A woven papermakers felt according to claim 1, further characterizedin that the fibres which coalesce at their crossing points arepredominantly polyamide fibres.

3. A woven papermakers felt according to claim 1, further characterizedin that the fibres which coalesce at their crossing points arepredominantly acrylic fibres.

4. A woven papermakers felt according to claim 1, further characterizedin that the fibres which coalesce at their crossing points arepredominantly polyester fibres.

References Cited by the Examiner UNITED STATES PATENTS 2,312,710 3/1943Gordon 139383 6 2,332,373 10/1943 Dorough et al. 28-73 2,375,597 5/1945Thomas 28-73 2,380,003 7/1945 Whitehead 28-73 2,381,061 8/1945 Kallrnann28-73 2,389,120 11/1945 Castellan 28-73 2,390,386 12/1945 Radford 28-732,450,948 10/1948 Foster 28-73 2,460,674 2/ 1949 Bihaly 28-73 2,685,1208/1954 Brant 28-73 2,771,659 11/1956 Ball 28-73 2,811,029 10/1957 Conner28-73 2,821,771 2/1958 Skeer 139-383 2,869,973 1/1959 Hubbard et a1.161-50 X 2,903,021 9/1959 Holden et al 139-383 2,905,585 9/1959 Hubbardet a1 8-13011 X 2,949,134 8/1960 Hindle et al. 139-383 FOREIGN PATENTS466,866 7/ 1950 Canada.

DONALD W. PARKER, Primary Examiner.

RUSSELL C. MADER, Examiner.

1. A PAPERMAKERS'' FELT CONSISTING OF MATERIAL WHEREIN UNCOATED WARP ANDWEFT YARNS ARE SO INTERCALATED AS TO PROVIDE A WATER-ABSORBENT STRUCTUREACCEPTABLE TO CONSTITUTE THE BASE FABRIC OF A CONVENTIONAL PAPERMAKER''SFELT, AND WHEREIN THE WARP AND WEFT YARNS ARE OF SUBSTANTIALLY THE SAMEDEGREE OF ROUNDNESS, IN TRANSVERSE SECTION, AS WHEN FRESHLY WOVEN, THEWARP AND WEFT YARNS BEING IN MAJOR PROPORTIONS, AT LEAST, OF SYNTHETICFIBRES; THE FELT POSSESSING DESIRABLE CHARACTERISTICS OF A CONVENTIONALWOOL FELT INCLUDING TENSILE STRENGTH, FLEXIBILITY AND PERMEABILITY TOWATER BUT POSSESSING GREATER ABRASIVE RESISTANCE AND HAVING A LONGERSERVICE LIFE THAN AN ALL-WOOL FELT, ONE FACE, AT LEAST, OF THE FELTCOMPRISING NAP FIBRES WHICH MASK THE WEAVE PATTERN AND COLLECTIVELYPROVIDE A SMOOTH SURFACE OF THE KIND DESIRABLE IN PAPER MAKING, THE FELTBING SUBSTANTIALLY DEVOID OF ANY SUBSTANCE OTHER THAN THAT COMPRISED INTHE ORIGINAL WARP AND WEFT YARNS, AS WOVEN, AND BEING FURTHERCHARACTERIZED IN THAT, PREDOMINANTLY AT POINTS AT WHICH CONSTITUENTFIBRES CROSS AND CONTACT ONE ANOTHER, THEY ARE SO COALESCED FROM A GELSTATE AS TO FORM PERMANENT BONDS THEREBY CONNECTING THE YARNS OF WHICHTHE UNITED FIBRES ARE CONSTITUENT ELEMENTS WHEREBY, ALTHOUGH THEMATERIAL RETAINS SUBSTANTIALLY THE SAME DEGREE OF FLEXIBILITY ANDPERMEABILITY WHICH IS POSSESSED WHEN FIRST WOVEN, IT IS COMPARABLE TO AFULLED WOOL FELT AS RESPECTS THE PERMANENT UNION OF CONSTITUENT FIBRES.